Lafollete-based Pyro Shows workers on Tuesday began setting up what will be a 20-minute Fourth of July eye-dazzler by securing about 300 “racks” containing 4- and 5-inch shells that will light up the Thursday night sky during the annual fireworks show on the Science Hill campus.

The pyrotechnics wizards arrived in Johnson City in the early morning hours and started securing what could be termed the launching pads for the show — the company’s second largest Fourth of July fireworks extravaganza in the state, bested only by an event in Nashville.

“It takes three days of setup for about 20 minutes of fireworks, but it’s worth it,” said Christopher Stiner, Pyro Works’ crew leader. “We have four guys out here today, and we’ll have five tomorrow. We don’t have a rain date for this, so it’s either go or no.”

A total of 4,000 shells will be launched Thursday night. Though technology plays a part in the process, it’s ultimately a “cue log,” a sheet containing launch times and sequences, and one individual who literally flicks the switch to initiate fireworks to do their thing.

“The log basically outlines the timing of the show,” Stiner said. “We give Pepsi a suggested song list, which they approve. A radio is initialized from a laptop computer which starts the sound track. The person hears that in a set of headphones.”

Stiner said an “electrical match” is lit which pushes electricity through a line. When the electricity hits the pyrotechnic compound, it causes a spark. That spark lights a timer fuse.

“It’s all hooked up to a firing board,” he said. “When the fuse is lit, the shell is launched that is set to explode when it reaches a certain altitude. They go up to 500 feet in the air. It’s very cool when you hear the crowd scream. That’s really cool.”

The company does about 250 shows during the Fourth of July holiday, and not all are on the same day. Stiner said his crew just did a show at Norris Lake and they will go from Johnson City to Bristol if the weather holds out. They have a show in Knoxville right after that.

“This is a choreographed show, meaning the explosions match up with music,” he said. “If it’s Lee Greenwood’s ‘God Bless the USA,’ we’ll use red white and blue. If it’s the song ‘Purple Rain’ (Prince), we use purple.”

The company was started in 1969 when the original owner and his friend were attending East Tennessee State University, said Michael Walden, Pyro Shows’ vice president of operations.

“Back then, they figured somebody would pay them to do little fairs in Tennessee,” Walden said. “It was named Pyro Shows in the mid-1980s. The company was one of the front runners of choreography — meaning when the song ‘Blue Suede Shoes’ was playing, blue fireworks would go off. That propelled the company to reach a pretty high place in the industry.”

In the 1990s, Walden was a chemistry teacher and guidance counselor for the Washington County School System. He started out with the company in 1993 as a technician and shot his first show in Johnson City.